What A-body did this 8 1/4 come out of?

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SGBARRACUDA

SGBARRACUDA

ROY
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So here is the st6ory. I buy some parts from a guy not real far from me. In all this stuff, I buy is a 8 1/4 rear that I was told came out of a 73 Duster 340 car. But here is where it gets a little weird. It's definitely is a 8 1/4, the casting number is 2852905, the spring perches are 43" apart which is correct for the A-body. But the brakes on this rear are 11" x 2"? Nowhere that I have been able to look show an A-body rear ever coming with 11" brakes? The housing measures correct for being out of a A-body, flange to flange is MOL 51 1/2". The bad news is it came with 2.45 gears which sucks, and the Sure Grip I got with it is for the 2.45 ratio or higher. So I'm looking for a 1/8" 8.25 ring gear spacer ,if anyone has one they want to sell. Any help would be appreciated.
 
Jeeps had 8 1/4 sure grip and all, nice ratios to boot. You can get them for around $100 up here.
 
If it was from a 1973 duster 340 car it would have had 3.21 gears in it....not 2.45....As stated the jeeps had 8-1/4 rears but usually they had 3.55 gears in them....The gears could have been changed over the years though.....Not sure of the brake size on the jeeps
 
As old as it is there is no telling what changes have been made to it. But the center to center on the leaf spring pads is 43" and I see no signs of them having been moved, so I feel sure it is an A-body 8 1/4. Maybe the 11" backing plates were put on there at some time. Does anyone know of anyone making the 8 1/4 ring gear 1/8" spacer these days?
 
I don't know of anybody making the spacers, Roy, but a good machine shop could whip you one out. They can use the face of the ring gear as a template.
 
From what I can find doing some research. You can use a GM 8.2 ring gear spacer and cut it down from .260 to .125 thickness.
 
Roy: Some 74 up Dusters had the 2.45 8-1/4 behind the Slant sixes. I saw one in a fairly rusty Duster around no too long ago. Also, I believe that the M Bodies had them too, but with the large perches for the isolator bushings.
 
Roy,

What's the measurement from wheel mount to wheel mount? If it's in the 57.25 range, it likely came from an A body.
 
crackedback said:
Roy,

What's the measurement from wheel mount to wheel mount? If it's in the 57.25 range, it likely came from an A body.
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I already have it a part. But the flange to flange ( where the brake backing plates bolt on) is 51 1/2" . Overall, from the end of the housing where the seal rides to the other is 54". The perches are 43" c to c and they are the standard style perches. I've got the wrong SG with it, one for 2.45. So I need to find or build a 1/8" ring gear spacer so I can install some 3.55's or 4.10's.
 
SGBARRACUDA said:
Ok, what is a FSM
Click to expand...

FSM=Factory Service Manual.

Tarvin890 and RustyRatRod got in a little bit of a tiff in another thread and Tarvin apparently think's he's being cute by suggesting an FSM on every single thread on the board. I didn't pick up on it at first but he's posted the same exact thing in like 10 different threads now. :roll:

Once again, the FSM would be quite helpful in rebuilding the 8 1/4, but almost useless for identifying what it actually came out of or shedding any light as to why it has 11" drums.
 
72bluNblu said:
FSM=Factory Service Manual.

Tarvin890 and RustyRatRod got in a little bit of a tiff in another thread and Tarvin apparently think's he's being cute by suggesting an FSM on every single thread on the board. I didn't pick up on it at first but he's posted the same exact thing in like 10 different threads now. :roll:

Once again, the FSM would be quite helpful in rebuilding the 8 1/4, but almost useless for identifying what it actually came out of or shedding any light as to why it has 11" drums.
Click to expand...

Your right, I noticed him on other threads posting FSM. That is why I finally asked.
 
SGBARRACUDA said:
Your right, I noticed him on other threads posting FSM. That is why I finally asked.
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No worries! ;)

So the 8.25 is 51.5" flange to flange? Interesting. That's the exact same measurement I pulled off of the BBP 7.25" that was in my '74 Duster originally. So, that probably is an A-body 8.25, especially if the perches look to be original at 43". The gear ratio wouldn't be matched up to a 340 car, but who knows. Same with the brakes. I'd say they were swapped out for the 11x2's, but man, if Commando66 has seen a couple more 8.25's with 11" brakes that may just have been the thing. Ma Mopar has been known to just add stuff if it was leftover. Like how all kinds of '71 A-bodies (and E's) got rim blow wheels without being optioned for them otherwise. They were discontinued for '72, so I guess they were just using them up.

It's interesting that the flange-flange measurement doesn't match the 8 3/4's, that screwed me up when I figured the backspacing for the first set of wheels I bought for my Duster, I assumed the BBP 7.25 had the same dimensions as the 8 3/4, but they don't. I wondered what the 8.25's were, seems like they might match the BBP 7.25.
 
Thats the answer I was mostly given when i asked a ??? so I took the advice... now have said FSM and its a wealth of information, most of the questions I see can be answered by the FSM. So now its an issue? Cant win.
 

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tarvin890 said:
Thats the answer I was mostly given when i asked a ??? so I took the advice... now have said FSM and its a wealth of information, most of the questions I see can be answered by the FSM. So now its an issue? Cant win.
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C'mon man.

Yes, the factory service manual is a wealth of information, and would provide answers for A LOT of the threads on here.

But, it's pretty obvious what's going on here. And most of the 10x you've posted "maybe a FSM would help" it actually WOULDN'T.

Which is what I take issue with. If it's in the FSM, awesome, you're actually being helpful. But if it's not, well, we know what opinions are like. And since I have quite a few factory service manuals, yes, I do have a pretty decent idea of what you can find in one, and what you can't. And your post about the FSM in this thread? Well, that info isn't in there. So, yeah, the FSM wouldn't help. Otherwise I wouldn't be asking SG if the 8.25 really is 51.5" flange to flange, because I'd already know what was in the FSM I already have.

So, can we keep this on topic?
 
the regulator question wouldnt help??? then why did someone post a schematic out of a FSM? I can go down each one one by one, it was good advice so Im passing it on.
 
72bluNblu said:
No worries! ;)

So the 8.25 is 51.5" flange to flange? Interesting. That's the exact same measurement I pulled off of the BBP 7.25" that was in my '74 Duster originally. So, that probably is an A-body 8.25, especially if the perches look to be original at 43". The gear ratio wouldn't be matched up to a 340 car, but who knows. Same with the brakes. I'd say they were swapped out for the 11x2's, but man, if Commando66 has seen a couple more 8.25's with 11" brakes that may just have been the thing. Ma Mopar has been known to just add stuff if it was leftover. Like how all kinds of '71 A-bodies (and E's) got rim blow wheels without being optioned for them otherwise. They were discontinued for '72, so I guess they were just using them up.

It's interesting that the flange-flange measurement doesn't match the 8 3/4's, that screwed me up when I figured the backspacing for the first set of wheels I bought for my Duster, I assumed the BBP 7.25 had the same dimensions as the 8 3/4, but they don't. I wondered what the 8.25's were, seems like they might match the BBP 7.25.
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Just sent an axle housing to Moser to be shortened. BBP axles are longer after the bearing, so the housing needs to be shorter to keep the same track width. Uses standard BBP wheels and backspace which keeps the wheels centered in the wheelwell, without thinking.
 
66fs said:
Just sent an axle housing to Moser to be shortened. BBP axles are longer after the bearing, so the housing needs to be shorter to keep the same track width. Uses standard BBP wheels and backspace which keeps the wheels centered in the wheelwell, without thinking.
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You're right about the axle stand off being different for the BBP axles, they are longer and switching to BBP axles (and brakes) from SBP axles does increase the track width, usually about 5/8" to 11/16" total, or ~5/16" per side.

But, the 51.5" flange to flange measurement doesn't keep the track width the same between the SBP 8 3/4" and the BBP 7.25 (or 8.25, apparently). The drum to drum measurement on the SBP A-body 8 3/4 is 57-1/8", the BBP 7.25" is ~56-5/8" drum to drum.

That still works out to a difference of 1/2", which doesn't sound like much, but it does change the backspacing a 1/4" if you want to keep the wheels in the same place. Not usually a big deal if you're running stock size tires/rims, but if you're going big that 1/4" is more than enough to cause interference.

The difference is even worse if you're moving from an A-body BBP 7.25 or 8.25 to an A-body 8 3/4 with BBP axles and brakes, that difference is 1.125", or 9/16" per side.
 
In the 73/74 change over Chrysler had a union strike with a vendor and had to use the "C" body 11''x2'' rear brakes on some "A" body cars to keep production rolling.I had a 74 Valiant with the 11'' rear brakes.That year they also were spec on taxi's and police cars that were "A" bodies.Mopar Action did a short blurb about it a few years back.
 
I'd measure both axles, add the numbers you get and add another 1.75-2". That should get you the rough mount to mount surfaces. If it's in the 57.5 range it's most likely an A body rear.
 
crackedback said:
I'd measure both axles, add the numbers you get and add another 1.75-2". That should get you the rough mount to mount surfaces. If it's in the 57.5 range it's most likely an A body rear.
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Funny you would say that. When I was measuring the rear, for the heck of it I did measure the axles. If you hook the measuring tape on the axle flange of the axle while it is laying on the bench, and extend the tape at a angle to the very end of the axle I got 27 7/8". So that would put it at 57 1/2 to 57 3/4 inches.
That with the perches @43" and they look like they were born there, I'm sure it is a A-body 8 1/4. It was the 11 x 2 brakes that threw me for a loop.
 
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